چكيده لاتين :
Internal erosion is a major threat to fill dams. The perfect filter approach to the design of filters
relates the permeability of filters to the size of particle that they will trap. It was devised following a
serious erosion incident at Balderhead dam. It approaches the matter from fundamentals, identifying
the size of the floc that will exist in clay fills and determining the permeability (as a measure of the
pore size) that will trap them. It does not depend on ‘self-filtering’. In addition to being a rigorous
method to design filters in new dams, the perfect filter relationship between permeability and filtering
capability can be used, to check the filtering capabilities of existing filters by measuring permeability
in-situ. Most importantly it can be used, by measuring their permeability in-situ, to assess the filtering
capability of the fills in the downstream shoulders of fill dams in which there are no formal filters. A
knowledge of the filtering capability of the fills in an existing dam can improve understanding of its
behaviour should internal erosion occur. If it can be shown that some, not necessarily all, of the
eroded material would be trapped, the failure process may be one of the formation of sinkholes, rather
than sudden catastrophic failure, and this allows time to save lives by releasing water in a controlled
manner from the reservoir and/or evacuating people out of the floodway downstream of a failing dam.
The perfect filter approach offers the means to improve on methods currently used to enumerate the
probability of failure of dams by internal erosion.
